Aqueous solutions of over 30% by weight formaldehyde, e.g., 30 to 80% by weight solutions, tend to be unstable and as a result precipitate formaldehyde polymers. This is indicated by the solution becoming cloudy and/or formation of deposits.
The art is well aware of this problem and many solutions have been proposed. Thus, formaldehyde solutions have been stabilized by diluting the concentration of formaldehyde, keeping the solution at high temperatures, or adding a stabilizer. Stabilizers that have been used include methanol, urea, melamine, organic colloids, e.g., methyl cellulose, graft polymers of vinyl acetate and ethylene glycol formaldehyde polyacetal, water insoluble acetals of polyvinyl alcohol, and other polymeric materials, e.g., U.S. Pat. Nos. 3,406,206; 3,518,313; 3,658,912; 3,137,736; 3,379,769; German Pat. No. 1,963,524 and Japanese Pat. Publication No. 4109/1962.
The use of any of the above stabilizing materials has not resolved the stability problem to the complete satisfaction of formaldehyde users. Some of the materials do not provide the desired degree of stabilization, particularly at low temperatures and at relatively high concentrations of formaldehyde. Others are insoluble in formaldehyde to such an extent that other materials must be used in conjunction with them, e.g., U.S. Pat. No. 3,518,313 teaches the use of anionic surface active agents in combination with water insoluble polyvinyl acetal polymers. Accordingly, there is still a need for an improved stabilizer for formaldehyde solutions.